HMF is an important furan compound. A large amount of materials and chemical intermediates can be made from HMF, which is reactive due to the reactive aldehyde group and hydroxymethyl group in molecule of HMF. And it is expected that HMF will become a new platform chemical. Moreover, HMF is an important intermediate between biomass-derived chemicals and petroleum-derived chemicals, since it can be produced from biomass and then converted to 2,5-dimethylfuran or hydrocarbon. So it will relieve the growing tension of the oil resources to a certain degree. It is reported that 2,5-dimethylfuran has a great potential to replace fossil fuels because it has many excellent properties as biofuel, such as high energy density and boiling point than that of bio-ethanol (Kunkes E L, Simonetti D A, Dumesic J A, et al. Catalytic Conversion of Biomass to Monofunctional Hydrocarbons and Targeted Liquid-Fuel Classes [J].Science 2008 322:417-421). In addition, 2,5-diformyfuran and 2,5-furandicarboxylic acid can also be obtained from HMF by oxidation. Wherein 2,5-diformyfuran can be used as starting material for synthesis of pharmaceuticals, polymer precursor and others chemicals, and 2,5-furandicarboxylic acid has a large potential as a replacement for terephthalic acid, which is obtained from fossil resources and widely used as a component in various polyesters, such as polyethylene terephthalate (PET) and polybutyleneterephthalate (PBT) (Pentz K W. Br.Pat. 2131014, 1984; Werpy T, Petersen G. Top Value Added Chemicals From Biomass, 2004). Additionally, HMF can be used as a pharmaceutical intermediate and flavor additive in cosmetic industry.
As a chemical platform, HMF has important applications in many industries, and more attention has been paid to it. Generally, HMF can be obtained by hexose dehydration under acidic catalyst. The reactant can be hexose, or oligosaccharides and glycans, even the biomass. The study of hexose dehydration into HMF is quite mature. According to the catalyst and reaction system, the reaction system can be divided into homogeneous catalysis system, ionic liquid system and heterogeneous catalysis system. In the homogeneous catalysis, some protonic acid such as HCl, H3PO4, H2SO4and some organic acids such as formic acid, levulinic acid are usually used as catalysts. However, the process associated with the problem of high corrosion, difficulty of separation and recovery, use of large amount of catalyst and so on. Thus more attention has been paid to ionic liquids system, and good HMF yields can be obtained in this reaction system. However, the high prices of ionic liquids and its unknown toxicity have limited the industrial application. The heterogeneous catalysis is one important part of catalytic disciplines for the easy separation and recovery of catalyst and environmental friendly. Now the problem about heterogeneous catalysis is that some solid acid such as zeolites is unstable in aqueous, i.e., the structure is easy to collapse, resulting in the decrease of catalytic activity. While the catalyst used in the present invention is stable in aqueous system, and its acidic strength will be enhanced. As natural green solvent, water is a good reaction medium for its low price which is desirable solvent for most of industrial production.